1. Field of the Invention
The present invention relates to a powder processing method for milling processing target powder by applying, in particular, a compressive force and a shearing force thereto, as a mechanical treatment for activating the processing target powder by applying a mechanical force thereto. The present invention relates also to a powder processing apparatus having an accumulating face on which the processing target powder is to be accumulated and a processing face disposed in opposition to the accumulating face and convexly curved, and a moving means for moving the accumulating face and the processing face along the accumulating face relative to each other. The present invention relates also to a method of manufacturing porous granulated substance formed by coagulation of the processing target powder and having a number of pores.
2. Description of Related Art
Conventionally, as the powder processing apparatus of the above-noted type, there is known an apparatus having a bottomed cylindrical container member for receiving processing target powder fed therein, a processing member which is disposed in opposition to an accumulating face, i.e. an inner face of the container member and which has a convexly curved processing face at the leading end thereof, and a rotational driving means (an example of “moving means”) for rotating the container member and the processing member relative to each other (see e.g. Japanese Patent Application “Kokai” No. 63-42728 (referred to as Prior-Art Document 1 hereinafter), Japanese Patent Application “Kokai” No. 6-134274 (Prior-Art Document 2 hereinafter), Japanese Patent Application “Kokai” No. 5-317679 (Prior-Art Document 3 hereinafter)). With such powder processing apparatuses as above in operation, as the rotational driving means is activated to cause the processing face formed at the leading end of the processing member to be moved relative to the accumulating face formed in the inner face of the container member so as to apply a compressive force and a shearing force to the processing target powder at the gap between the accumulating face and the processing face, thus effecting a milling treatment to the processing target powder, for example.
Further, the above-described Prior-Art Document 3 discloses a technique in which the above-described powder processing apparatus is employed for milling and mixing, by applying strong compressive and shearing forces to a mixed powder thereto, the powder mix being obtained by adding fine ceramics powder of e.g. silicon nitride or zirconia to a metal powder of e.g. stainless steel, thereby compounding the metal powder and the fine ceramics powder in such a manner that a coating layer comprised of the metal powder and the fine ceramics powder is formed on surfaces of cores of metal particles.
Also, as a compound powder obtained by compounding processing target powder with another substance, there is known nitrogen-containing titanium oxide powder obtained by compounding titanium oxide powder with nitrogen element. And, it is known that this nitrogen-containing titanium oxide powder acts as a photocatalyst.
In this way, as a powder processing method for manufacturing a compound powder by compounding a processing target powder with another substance, there are known e.g. a method including the steps of stirring and mixing titanium oxide powder and urea as a nitrogen compound for causing the urea to be adsorbed on the titanium oxide powder and then heating them together (see e.g. Japanese Patent Application “Kokai” No. 2002-154823 (referred to as Prior-Art Document 4 hereinafter)), a method comprising sputtering titanium oxide powder as a target in a nitrogen-containing gas (see e.g. Japanese Patent Application “Kokai” No. 2000-140636 (referred to as Prior-Art Document 5, hereinafter)), a method comprising effecting a nitrogen plasma treatment on titanium oxide powder (see e.g. Prior-Art Document 4 and Japanese Patent Application “Kokai” No. 11-43759 (referred to as Prior-Art Document 6 hereinafter)), and so on.
In the case of the powder processing methods described in the above-described Prior-Art Documents 1-3 using the powder processing apparatus in compounding a processing target powder such as titanium oxide powder with another substance such as nitrogen, thus manufacturing compound powder, while it is possible to render the surface of the processing target powder to a state of a relatively high activity by milling the powder, it has been difficult for any of these methods alone to compound the processing target powder with another substance.
Also, in the case of the powder processing method described in the above-described Prior-Art Document 4, in order to compound nitrogen contained in urea with the titanium oxide powder, it is necessary to heat the entire titanium oxide powder to e.g. 500° C. for 30 minutes in advance. Hence, the method requires e.g. a heating furnace, thus complicating the processing apparatus and requiring a vast amount of processing time as well.
Further, in the case of the powder processing methods described in the above-described Prior-Art Documents 4-6, if there exists organic substance adsorbed on the surface of the processing target powder such as titanium oxide, this will hinder the compounding of another substance to the metal oxide powder, thus inviting deterioration in the yield. Moreover, e.g. the sputtering treatment alone could not manufacture the compound power in an uniform and efficient manner.
Also, there is known porous granulated substance having a number of pores, hence usable as a heat insulating material with restriction of heat transfer by these pores or as a sound absorbing material with restriction of transmittance of sound waves. And, it is also known that if the pores of such porous granulated substance are formed extremely small, movement of air molecules will be restricted and entrance of air molecules into these pores will also be restricted, so that super low heat conductivity and super high sound absorbency can be achieved. Further, the porous granulated substance having such small pores can be expected to be used as a separating membrane for various components.
Such porous granulated substance can be manufactured by causing fine processing target powder to coagulate by applying a compressive force thereto.
However, in the case of the above-described method of manufacturing porous granulated substance, the application of a compressive force to the processing target powder alone sometimes fails to realize good coagulation of the processing target powder.
Also, when the powder processing apparatus disclosed in any one of Prior-Art Documents 1-3 is used for milling the processing target powder by applying a compressive force and a shearing force to the powder at the gap between the accumulating face and the processing face opposed thereto in association with a relative movement therebetween, an active face such as a newborn face can be formed on the surface of the processing target powder. This is believed to facilitate the coagulation of the processing target powder. As a matter of fact, although a certain degree of coagulation of the milled processing target powder is possible, it was difficult to achieve such degree of coagulation as enables the powder to be used as the porous granulated substance.